High vacuum coating machine, coating machine is the most widely used in the production of vacuum conditions. Its related components and components: mechanical pump, booster pump, oil diffusion pump, condensate pump, vacuum measurement system.
I detail the composition and working principle of each part.
First, the main vacuum chamber
According to the product processing requirements are different, the size of the vacuum chamber is not the same, the application of the most have diameter 1.3m, 0.9m, 1.5m, 1.8m, and cavity made of stainless steel material production, requires no rust, solid and various parts of the vacuum chamber is connected with the valve, which is used to connect the suction pump.
Two, auxiliary pumping system
The exhaust system with diffusion pump + mechanical pump + + roots pump cryotraps + polycold "
Exhaust process: mechanical pump the vacuum chamber pumped to less than low vacuum state about 2.0*10-2PA, diffusion pump subsequent vacuum provides premise, after the diffusion pump vacuum, mechanical pump and fit oil diffusion pump which are connected in series, in such a way complete pumping action.
The exhaust system is an important part of the vacuum system of the coating machine, mainly consists of three parts: mechanical pump, booster pump (mainly introduced Luo Cibeng), oil diffusion pump.
Mechanical pump: also called pre stage pump, mechanical pump is the most widely used a low vacuum pump, it is oil to keep the sealing effect and rely on mechanical methods are constantly changing the pump suction cavity volume, was pumping gas in the container volume constant expansion to obtain vacuum.
Mechanical pump has a lot of kinds, commonly used a slide valve type (this is mainly used in large-scale equipment), reciprocating piston, stator and rotary vane (this is currently the most widely used. This paper mainly introduces) four types.
Mechanical pump is often used for sucking air from the dry, but not pumping in addition to containing high oxygen content, explosive and corrosive gas, mechanical pump is generally used to pumping gas permanent, but to moisture without good effect, so it can't pumping in addition to water vapor. Rotary vane pump stator, rotor, shrapnel and other components. The main function of the rotor in the stator but with different stator mandrel, like two inscribed circle, the rotor slot is provided with two pieces of shrapnel, bombs and pieces, in the middle is provided with a spring, to ensure the shrapnel tightly attached to the inner wall of the stator.
Its two shrapnel alternating plays the role, on the one hand from the air inlet to breathe in the air, on the other hand compression has been sucked into the gas, gas discharged from the pump. Each rotation of the rotor one week, the pump completed two times and two times the exhaust gas. When the pump rotates clockwise, the rotary vane pump continuously through the air inlet gas, and continuously discharge from the exhaust port outside, to achieve the purpose of pumping gas container. In order to improve the ultimate vacuum pump, pump stator immersed in the oil inside, inside the gap everywhere and harmful space often keep enough oil, to fill the gap, so that the oil played a role in lubrication on the one hand, on the other side and the sealing and plugging the gap and harm the space effect, to prevent gas molecules through a variety of channels counter flow to the low pressure of the space to.
Mechanical pump from the beginning of the work, and its main parameters are the ultimate vacuum, pumping rate, this is an important basis for the design and selection of mechanical pump. A single pump can pump the container from the atmosphere to the ultimate vacuum of 1.0*10-1PA, a dual stage mechanical pump can pump the container from the atmosphere to 6.7*10-2 PA, or even higher.
Pumping rate, is refers to the rotary vane pump according to the rated speed operation, the unit time can exhaust gas volume, can be calculated by the formula:
FS said suction cavity cross-sectional area, l said cavity length and coefficient of said rotor rotates one week two exhaust process, vs said when the rotor in a horizontal position, suction end. At this time the cavity volume maximum speed n.
Mechanical pump exhaust effect and the rotational speed of the motor and the belt tightness relationship, when the motor belt is loose, when the motor speed is very slow, the mechanical pump exhaust effect will become worse, so to regular maintenance, inspection, mechanical pump oil sealing effect, we also need to constantly check, oil is too small, amounting to less than the sealing effect, pump will leak. Too much oil, the suction holes to plug, to suction and exhaust, in general, under the oil level online 0.5 cm.
Booster pump is also called lobed element pump: it is with a pair of synchronous high-speed rotation of the bilobed shaped or lobed rotor mechanical pump, due to its working principle and roots blower are the same, and can call the roots vacuum pump, the pump in 100-1 PA pressure range have greater pumping speed, it makes up for the shortcoming of this mechanical pump exhaust ability is insufficient, this pump is not from the atmosphere began to work, can not be directly discharged into the atmosphere, its role is only increase the inlet and exhaust ports between the pressure difference and the rest of the need mechanical pump to complete. Therefore, it must with the mechanical pump as the pump before the class.
Mechanical pump in the use of the process, we must pay attention to the following questions:
1, mechanical pumps to be installed in a clean and dry place.
2, the pump itself should be kept clean and dry, the oil in the pump has a sealing and lubricating effect, so to be added in accordance with the provisions.
3, to periodically replace the pump oil, the replacement of the time to discharge first before the waste oil for a period of at least three months to six months to replace a.
4, in accordance with the instructions to connect wires.
5, before the mechanical pump to stop working to close the intake valve, and then power outage and open air valve, the atmosphere through the air inlet into the pump.
6, pump during operation, the oil temperature can not exceed 75 degrees Celsius, otherwise it will be because the oil viscosity is too small to result in mifengbuyan.
7, or regular indecent mechanical pump belt tightness, motor speed, roots pump motor speed, and sealing ring sealing effect.
Oil diffusion pump: mechanical pump limit vacuum only 10-2 PA, when to reach 10-1 PA, the actual pumping speed is only the theory of 1/10, if you want to get a high vacuum, then you must use oil diffusion pump.
As oil diffusion pump is the first to obtain a high vacuum pump, its cost is cheap, easy to maintain, the use of a wide range, so this paper will focus on the discussion.
Oil diffusion pump pressure range is 10-1 PA -10-7 PA, it is the use of gas diffusion phenomenon to exhaust, it has a simple structure, easy to operate, pumping speed large (maximum can reach 10+5 liters / sec), etc.. Oil diffusion pump is mainly composed of pump shell, nozzle, diversion pipe and heater, which mainly add diffusion pump oil (Japan's model is D-704#), according to the number of nozzles can be divided into single pump and multi-stage pump.
Diffusion pump at the bottom is stored in the oil diffusion pump, the upper part of the air inlet and the right side of the lower air outlet, in the port by a mechanical pump to provide pre pressure, the mechanical pump acts as a booster pump.
When the diffusion pump oil is heated by electric furnace, the oil vapor provided by the pre pressure, the mechanical pump to act as a pre pump. When the diffusion pump oil is heating, oil vapor generated along the diversion pipe through the nozzle ejected down umbrella. Outside the nozzle due to the vacuum mechanical pump to provide 1-10-1 PA in the, so oil steam can be ejected from a distance, constitute a to the air outlet direction of movement of the jet. Jet finally hit by cooling water cooling wall of the pump, condensation liquid, flowing into the evaporator, namely by the evaporation of oil jet -- setting and repeat the cycle to achieve pumping.
On both sides of the interface of a steam from the inlet into the pump of gas molecules, once fall into the steam flow, will get the downward movement of momentum down flew the jet with high velocity (about 200 meters / seconds), high density and diffusion pump oil with high molecular weight (300-500) and therefore can effectively take away the gas molecules, so in the jet, the gas molecules are not possible long-term retention, and the interface of jet, was pumping gas has great concentration of poor, it is because of this concentration difference to be pumping gas continuous across the interface and diffusion into the jet, was taken to a port in the exit by the mechanical pump.
Diffusion pump oil vapor pressure is an important factor in the ultimate vacuum pump, so as far as possible the selection of saturated vapor pressure of the oil pump, its chemical properties better.
Diffusion pump can not be used alone to pump gas, the general requirements of the maximum outlet pressure of the pump is 40 PA. Diffusion pump pumping speed decided to in the size of the first stage nozzle and the pump inlet diameter annular area, pumping speed is not a constant value, but with the inlet pressure changes, when the pressure in 10-2 ~ 10-3 Pa., diffusion pump pumping speed is the fastest, when the pressure is less than 5 * 10-4 pa, diffusion pump pumping speed is minimum, almost no smoke gas ability (at that time, the inlet pressure is higher, the air density is bigger, the steam flow is formed in the high-speed jet of not to block the air back diffusion, so the pumping speed decreased).
Diffusion pump before installation should be cleaned before they can into the spread of oil, oil in the heat before, must first to pump vacuum, down to the diffusion pump oil cooling to 60 ~ 70 degrees Celsius to close before pumping finally closed cooling water.
Because the oil diffusion pump is unable to stop the oil back to the chance, so there is no way to ensure clean precision products 100%, in particular, the semiconductor industry, so there is "high vacuum condensate pump + low mechanical vacuum pump" composed of oil free vacuum system, composed of condensate pump exhaust system not only exhaust efficiency is high, and effectively guarantee the vacuum cavity clean, ensure product quality (to avoid product contamination and enhance the adhesion between the coating and the substrate), but its maintenance cost is very high, expensive, so the penetration rate does not have the oil diffusion pump is widely.
I am in the process of work, the use of the use of condensate pump exhaust system, it is explained in this.
Cryocondensation pump: it is the low temperature surface to condensed gas molecules to achieve pumping a pump, is the ultimate vacuum highest pumping the maximum speed of the pump.
The working principle of the condensate pump: it is mainly the condensation of the gas at the low temperature, the cold trapping and the physical low temperature adsorption.
Low temperature condensation: according to the characteristics of various gases, using liquid helium or helium cooled refrigeration cycle.
Cold trapping: is not gas is set the phenomenon of gas collector, usually carbon dioxide, water vapor, nitrogen, compressed air and other gas first the formation of frost, in low temperature surface adsorption layer formed, so as to achieve the purpose of gas adsorption, cryogenic pumps pumping in addition to the gas mixing effect than pumping single effect is good and it is for this reason.
Cryogenic adsorption: refers to the effects of low temperature on the surface of the adsorbent in the adsorption of gas, due to the strong interaction between the gas molecules and adsorbents, so it can be to vapor pressure condensing surface temperature than its saturation vapor pressure is low level. Adsorbent is usually activated carbon.